A remarkable achievement by the Atlantis expedition (1947) of the Woods Hole Oceanographic Institution, under the leadership of Professor Maurice Ewing, was the recovery of several hundred pounds of boulders from depths approaching 2,500 fathoms over the Mid-Atlantic Ridge. Some of these boulders are of limestone and will be described elsewhere, but a large proportion consists of eruptive rocks referable to the following groups: (I) holocrystalline gabbroic rocks, (2) basalts (pillow lavas) with and without olivine, and (3) serpentines. Table i gives the latitude and longitude of each station where these boulders were collected, together with the depth and the kind